1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to slot antennas used in high-power applications.
2. Description of the Related Art
The individual antenna elements of a wide-scan phased array antenna (e.g., one capable of scanning very wide angles such as +/-45.degree.) must typically be spaced very close together. More specifically, the individual antenna elements must generally be spaced approximately one-half of a free-space wavelength apart from one another. There are a variety of antenna elements that are of such compact design. However, none of the presently available antennas, compact enough for use in a wide-scan phased array antenna, are capable of handling very high average power levels while simultaneously providing very accurate polarization, e.g., circular polarization, over a very large angular region (e.g., +/-50.degree. in both planes). In this connection, there are a number of applications, including high-power wide-scan phased array antennas, that require an extremely compact antenna design that satisfies these constraints. The following brief review of the presently available antenna technology should serve to illustrate the limitations and shortcomings thereof. Circularly polarized patch antennas can be made smaller than one-half of a free-space wavelength, but only through the use of a dielectric, thereby rendering the patch antenna inadequate for high power applications. A circularly polarized ridged waveguide antenna having a slot formed in a surface thereof can be made smaller than one-half of a free-space wavelength. Although such an antenna design can handle high power levels, it is not capable of providing accurate circular polarization.
A rectangular cavity-backed slot antenna can be constructed that can handle high power levels (i.e., no dielectric is required). However, the cross-sectional dimensions of the cavity must be greater than one-half of a free-space wavelength (typically, 7/10th of a wavelength on edge) for the device to be operative. The reason that the dimensions of the cavity must be greater than one-half of a free-space wavelength is due to the fact that in order for the cavity to resonate, the rectangular dimensions must be equal to one-half of a guide wavelength, which is longer than the free-space wavelength.
The size of a conventional cavity-backed slot antenna can be reduced by filling the cavity with a dielectric material, but this introduces substantial losses and renders the antenna inadequate for high average power applications.
Other known antenna designs include those disclosed in U.S. Pat. No. 3,573,834, issued to McCabe et al.; U.S. Pat. No. 4,130,823, issued to Hoople; U.S. Pat. No. 4,132,995, issued to Monser; and, U.S. Pat. No. 5,461,393, issued to Gordon. However, the antennas disclosed in these patents are either too Large, have poor circular polarization performance, and/or can not handle high power levels.
Thus, there is a need in the art for an extremely compact antenna that is capable of handling high power levels and providing very accurate polarization, e.g., for use in high-power applications that require radiation of very accurate circular polarization over a very large angular region (e.g., +/-50.degree. in both planes), such as in wide-scan phased array antennas.